1. Field of the Invention
The present invention relates to communication terminal apparatuses and control methods thereof which can be connected to an integrated service digital network (hereinafter, which will be referred to as the ISDN) and, more particularly, to a communication terminal apparatus and its control method which allow the realization of parallel operation of a plurality of communications with use of a plurality of data channels allocated to each line of the ISDN.
2. Description of the Related Art
A general communication terminal apparatus such as a facsimile equipment connected to a public telephone line or a DDX line, can execute only one of voice and image data communications or alternately execute the voice and image data, that is, can perform only so-called half duplex operation.
This is because the above public telephone line or DDX line can basically have a band corresponding only to one-channel information, which results in that, the simultaneous transmission of both the voice and image data leads to data deterioration and transmission ate reduction.
As the ISDN is put to practical use these days, the communication apparatus itself connected to the ISDN has been uniquely developed in the practical use of communication services.
As already known, the ISDN is an integrated digital network which integrally handles such service apparatuses different in contents to be handled as telephone sets, telex equipment and facsimile equipment and which has a plurality of channels for each ISDN line.
An attempt has ben made to realize the simultaneous transmission of voice and image data with use of the plural data channels of the ISDN line.
With the communication terminal apparatus connected to the ISDN, however, if a call demanding the reception of image data comes into the apparatus through second one of the plural data channels of the ISDN line, for example, during the reception of image data of the apparatus through first one of the data channels (during operation of an image printer in the apparatus), then the apparatus, in answer to the demand of reception of the new image data, can only send a busy tone back to the party terminal because the image printer is in operation, and thus the call from the party terminal becomes useless.
Further, for example, when the communication terminal apparatus, which is talking with the party through the first data channel of the ISDN line, receives an incoming call demanding a speech, i.e., a voice demanding call through the second data channel; the apparatus, in response to this new speech demand, can only send a busy tone indicative of the busy destination party back to the party terminal a busy tone, thus resulting in that the call from the party terminal becomes useless.
In this way, the prior art communication terminal apparatus has had problems that, when the apparatus receives the new image data demand through the second data channel during execution of the image data trough the first data channel and when the apparatus receives the new speech demand through the second data channel during talk through the first data channel, the apparatus cannot execute the new image and speech demands respectively, inevitably involving the reduction of its communication efficiency.
The present invention also provides a communication terminal apparatus and its control method which allows the simultaneous realization of a plurality of communications.
It is, accordingly, an object of the present invention to provide a communication terminal apparatus and its control method which, when receiving a new image data demand through a second data channel during execution of image data through a first data channel, can accept the new image demand and can perform different-direction full duplex communication over the image data, thus increasing its communication efficiency.
It is another object of the present invention to provide a communication terminal apparatus and its control method which, when receiving a new incoming voice signal through a second data channel during talk through a first data channel, can execute the new voice signal without sending a busy tone back to the party terminal, with a good communication efficiency.